Lizbeth Hedstrom

Degrees

Brandeis University, PhD
University of Virginia, BS

Profile

My laboratory uses approaches derived from both chemistry and biology. Projects include problems in inhibitor design, enzyme catalysis, protein degradation and the mechanism of visual disease. Techniques vary with the particular project, and can entail molecular biology, organic synthesis, protein crystallography and NMR spectroscopy as well as protein purification, enzyme kinetics and mutagenesis. Our ongoing projects are outlined below. For more information, please see the lab website.

Dynamic structural determinants of reaction specificity. Understanding of how structure determines function is a central challenge in biochemistry. The IMPDH/GMPR family provides a striking example of how subtle differences in protein sequence, and hence in structure, can profoundly change reaction outcomes. These enzymes share a common set of catalytic residues and bind the same ligands with similar affinities.

The reactions utilize the same covalent intermediate, yet with markedly different outcomes. IMPDH performs a hydride transfer reaction followed by a hydrolysis reaction, and a protein conformational changes rearranges the active site to accommodate both reactions. GMPR performs a deamination reaction followed by a hydride transfer reaction. In this case, the cofactor has a different position in each reaction. We are now trying to understand what structural features determine this very different dynamic behavior. Our long-range goal is to develop computational models that accurately recapitulate and quantitatively predict the catalytic properties of enzymes in the IMPDH/GMPR family. This work will advance the field of computational chemistry and provide important insights into how enzymes work. This work is a collaboration with Wei Yang of Florida State University.

Targeting a prokaryotic enzyme in a eukaryotic pathogen. The protozoan parasite Cryptosporidium parvum is an emerging opportunistic pathogen and potential bio-warfare agent. The C. parvum oocyte is resistant to the usual methods of water treatment, which has caused spectacular outbreaks such as the infection of 40% of the inhabitants of Milwaukee in 1993. C. parvum is resistant to the usual antiparasitic drugs and currently used chemotherapy is ineffective. In collaboration with Boris Striepen at UGA, we have been engaged in a medicinal chemistry program targeting C. parvum IMPDH. Curiously, the parasite obtained its IMPDH gene via horizontal transfer from a bacteria, so the parasite enzyme is very different from its host. We have a collection of low nanomolar inhibitors of the parasite enzyme, some of which show promising in vivo antiparasitic activity. These compounds also inhibit IMPDHs from pathogenic bacteria such as Mycobacterium tuberculosis, Staphylococcus aureus, Helicobacter pylori and Francisella tularensis. We are now investigating the potential of these compounds as broad spectrum antibiotics. This work is a collaboration with Joanna Goldberg at Emory and Barb Mann at UVA.

Small molecule strategies to modulate protein levels. A small molecule that induces the selective degradation of endogenous proteins would clearly be a tremendously useful tool for probing protein function and an exciting new approach for chemotherapy. We serendipitously discovered a small molecule tag (Boc3Arg) that induces the degradation of target proteins. This tag both localizes the target protein to the 20S proteasome and activates the 20S proteasome. We have also discovered small molecules that block protein translation by interfering with mTORC1 signaling. Modulation of the ubiquitination pathways provides another strategy to induce targeted protein degradation, and we have discovered that the anticancer compounds found in broccoli and other cruciferous vegetables are deubiquitinating enzyme inhibitors. These compounds may be useful in applications ranging from therapy for cancer and diabetes to increasing lifespan.